Rollup merge of #82351 - notriddle:docs-meta-description, r=jyn514

Use the first paragraph, instead of cookie-cutter text, for rustdoc descriptions

Partially addresses #82283.

src/librustdoc/html/render/mod.rs

@@ -1548,7 +1548,10 @@ impl Context<'_> {
         }
         title.push_str(" - Rust");
         let tyname = it.type_();
-        let desc = if it.is_crate() {
+        let desc = it.doc_value().as_ref().map(|doc| plain_text_summary(&doc));
+        let desc = if let Some(desc) = desc {
+            desc
+        } else if it.is_crate() {
             format!("API documentation for the Rust `{}` crate.", self.shared.layout.krate)
         } else {
             format!(